Conventionally, when a motor vehicle is loaded with a large quantity of loads or a load with a considerably large length, a seat back of its rear seat is folded onto the upper face of a seat cushion of the rear seat, so as to expand a load-carrying platform or cargo deck. Further, Publication No. 46-4489 of examined Japanese Utility Model Application discloses a technique for further expanding the load-carrying platform, by rotating the seat cushion forward about a hinge provided at its front end, lower portion to bring it into an upright position, and then leaning the seat back forward so that the rear seat provides a flat plane that is substantially flush with the load-carrying platform behind the rear seat.
In addition, Publication No. 2-5613 of examined Japanese Patent Application discloses a double hinge structure including a link mechanism in which one end of a link arm is connected to the front, lower portion of the seat cushion to be rotated, and the other end of the link arm is provided on a seat floor and pivotably supported by the floor. With this double hinge mechanism, the seat may be selectively placed in a seating position for normal use in which the seat cushion is kept in a substantially flat state, or a first folded position in which the seat back is rotated or leaned forward onto the upper face of the seat cushion and kept in the folded state, or a second folded position in which the seat cushion is raised to the uprighrt position and the seat back is leaned forward into a space on the seat floor that is generated by raising the seat cushion.
The above-described conventional seat structure, which is proposed to flip the seat cushion forward into an upright position, cannot form a flat, extensive load-carrying floor that extends from the rear platform or cargo deck to an instrument panel in the front part of the vehicle, thus making it difficult to mount a load having a large length in the vehicle. Also, in the known seat structure, passengers cannot lay down comfortably for a break.
In view of the above, it has been proposed to flip over the seat cushion of the rear seat and set it in position on a floor panel, and combining the rear seat with the front seat to form a more useful space in the interior compartment of the vehicle.
If the known double hinge structure, which is rotatably supported about two axes as described above, is applied for the above purpose, however, the seat cushion undergoes irregular movements when rotating about the double hinge structure, thus requiring careful operations where the seat cushion must be supported at its both sides. Thus, the operation to flip over the seat cushion becomes undesirably unsafe and complicated. Further, pivotal support portions of the double hinge structure may be damaged due to distortion thereof in the lateral direction during flipping-over of the seat cushion.
The rear seat may be divided into two sections in the ratio (6:4, for instance) that makes the width of one section larger than that of the other section. In this case, the section having the smaller width may be flipped over without causing any problem, but the other section having the larger width cannot be successfully flipped over and set in position since it may interfere with a console box or the like that protrudes toward the rear seat in the middle of the interior compartment. In this case, too, the seat structure cannot fully meet the requirement to allow the passengers to lay down on the seats.